stumbles replaced fuel pressure regulator only DTC pointed to low side of mass air flow. Pulled it wiring check as per shop manual ok the stumble is now less frequent now. Also seems to relate to AC set to on. the clutch pulley is noisy when off ok when on. shop manual states a relationship between bad ac clutch diode and engine stumble. 1) can clutch be replaced w/o pulling ac compressor? 2) suggestions on debugging the stumble? Thanks to all and happy motering.

You pulled WHAT wiring checks? Voltage? Ohms? Wriggle?
To me, the checks which are most meaningful are the voltage measurements of the MAF while the engine is running. I, then check the chart to see if the voltage indicates the expected grams per second air flow for a particular throttle setting and engine load.